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Hypothermia Helps Cardiac Patients to Live Longer

08.04.2002

Approximately 375,000 Europeans suffer cardiac arrest every year – often with fatal consequences. Even upon successful resuscitation, several patients suffer severe and irreparable brain damage. One in seven patients could be saved and the amount of serious damage resulting from cardiac arrest could be drastically reduced by reducing the body temperature of those affected to between 32 and 34 degrees in the first 24 hours following the cardiac arrest. Such are the results of a Europe-wide study, in which the University of Bonn was involved. The findings were originally published in the New England Journal of Medicine (N Engl J Med, Feb. 21, 2002; vol. 346 (8) pgs. 549-556).

The medics investigated a group of 275 patients whose blood circulation was interrupted for between 5 and 15 minutes following a cardiac arrest brought on by ventricular fibrillation. The body temperature of half of those affected was lowered to between 32 and 34 degrees within four hours of the cardiac arrest. This was done in a special bed by circulating cold air around the patients` bodies. The cooling process was complete after 24 hours, and the body temperature then brought back to normal. The doctors did not reduce the body temperature of the other half of the patients. Otherwise, both groups were treated identically. "Six months after the cardiac arrest, 55 per cent of the patients exposed to low temperatures showed only very little or no impairment of the brain functions, 4 per cent showed severe neurological damage, 41 per cent had died", reports Dr. Peter Walger, director of the intensive care unit of the Medical Polyclinic at the University of Bonn and one of the co-authors of the study, summarising the findings of the study. "On the other hand", he continues, "we observed very little or no damage among only 39 per cent of the patients not exposed to low temperatures. Of these, 6 per cent had suffered severe brain damage, and 55 per cent had died."

But how do low temperatures protect patients? After the blood circulation has been interrupted for several minutes, free radicals start forming in large amounts in the body. These may start a chain reaction in the resuscitated patient which ends in irreparable brain damage. This adds to the damage caused by the lack of oxygen. Low temperatures appear to slow down both the formation of radicals and also the metabolic processes which they trigger. Investigations into the effect of exposure to low temperatures on the survival chance and the long term damage among resuscitated patients were carried out as early as the 1950s and 1960s. The findings at that time were, however, contradictory, so further investigations were not conducted until the 1990s – first on animals, and then on small groups of patients.

The large number of patients involved in the present study adds weight to its findings. In addition, the findings of an Australian work group published at the same time also reveal similar results und so support the importance of this method of treatment. According to Dr. Walger: "Each year, approximately 375,000 Europeans suffer cardiac arrest; 30,000 of these meet the conditions which we laid down for our study. If these 30,000 patients were all exposed to low temperatures according to the method described, severe neurological damage could be prevented in up to 7,500 cases.“

The New England Journal of Medicine found the results of both studies so impressive that they devoted an editoral and a separate overview article to the theme "Hypothermia following cardiac arrest“. Although further studies are necessary, the authors are already recommending light hypothermia for survivors of a cardiac arrest – as soon as possible and for at least twelve hours.

The Medical Polyclinic was one of eight European centres, which participated in the EU-sponsored study. The doctors worked in close co-operation with the Bonn emergency doctor system, directed by Dr. Matthias Fischer of the clinic for Anesthesiology und special intensive care medicine of the University of Bonn. The anesthesiological intensive care station of the Waldkrankenhauses in Bad Godesberg was also involved in the study.

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